This invention relates generally to illumination devices used in the entertainment field and, more specifically, to lighting fixtures emitting a controllably steered light beam. Ideally, the light beam must be continuously steerable through a full circle, i.e. 360 degrees of azimuth angle, and through a full 360 degrees of elevation, from horizontal to vertical in both directions.
In the past, two-axis beam steering has been accomplished either by turning an entire fixture or lamp housing, or by use of a single mirror. Movement of the entire fixture limits the positioning speed because of the relatively high inertia of the fixture. Also, movement of the lamp results in lower lamp life because of motor vibration and continual movement. Such devices also have angular limits on the extent of movement of the beam about the azimuth and elevation axes.
Some of these difficulties are diminished by the use of a mirror to steer the beam, as disclosed in U.S. Pat. No. 4,697,227 to Callahan. In the Callahan device, a light beam is deflected through a ninety-degree angle by a plane mirror oriented at 45 degrees to the optical axis of the beam. A motor rotates the mirror about the optical axis, to deflect the beam to any azimuth angle in a plane perpendicular to the optical axis. Deflection in elevation is achieved by rotation of the entire fixture assembly about an axis perpendicular to the optical axis. Therefore, although steering about one axis is relatively quick and responsive, steering about the other axis is subject to inertia limitations and to angular movement limitations imposed by having motors that must be bodily moved to steer the beam.
Ideally, a two-axis beam steering system should be able to deflect a light beam through a solid angle equivalent to a complete sphere, without angular limitations except for any dead zone or shadowing caused by the presence of system components. Furthermore, steering of the beam should be accomplished without bodily movement of drive motors or other bulky components. The present invention is directed to these ends.